The field of the invention is headphones, and particularly, high quality headphones which are produced for the high fidelity market.
One of the most difficult problems of designing a headphone, or stereophone, is to provide an acoustic transducer which will faithfully reproduce frequencies over the entire audio spectrum. When a single acoustic transducer is employed in each ear cup assembly, compromises are made either in its low frequency or high frequency response. For this reason manufacturers typically offer a family of stereophones in which these compromises are varied to provide sounds which conform to the tastes of different listener groups.
The designers of loudspeakers have long recognized the need for more than a single acoustic transducer to reproduce the entire audio spectrum. Quality loudspeakers may contain from two to five separate acoustic transducers, each designed to operate over a specific portion of the audio spectrum. Crossover networks are employed to distribute the applied audio signal to the proper acoustic transducer and these typically include circuits comprised of resistors, capacitors and inductors.
Prior attempts at providing more than one acoustic transducer in a headphone cup assembly have not been successful. When two dynamic transducers have been employed the size and weight of the headphone becomes excessive, particularly when a crossover network is used. Electrostatic transducers have been used in combination with dynamic transducers, but these require expensive and cumbersome high voltage power supplies and crossover networks.